The invention relates to vehicle transmissions, namely chains of members transmitting the rotational movement of the engine to the wheels of the vehicle, which members comprise a gearbox, a rear axle and a double jointed cardan shaft transferring the torque from the gearbox to the rear axle while permitting relative transverse movements thereof.
It relates more particularly, among such transmissions, to those equipped with an electric eddy current retarder adapted to exert thereon a braking torque at the desired times, said retarder comprising, on the one hand, an annular inductor stator cantilevered on the gearbox casing of the vehicle by means of an appropriate frame and, on the other hand, a rotor comprising two armature discs made from a ferromagnetic material which surround the stator and are both supported by a part itself cantilevered on a stub shaft inside the casing, each disc being fixed for this purpose, via a circle of arms forming ventilation fins, with a ring which is in its turn fixed to said part.
In known embodiments of transmissions of the kind in question, the part on which the two rings are mounted is generally a special insert plate which is fixed, on the one hand, on a "gearbox flange" fixed on a stub shaft inside the casing of the gearbox and, on the other hand, on the axial side opposite said sub shaft, on an end flange of the adjacent cardan joint.
It should in fact be noted that it is not in practice possible to mount the rotor rings directly on the gearbox flange, for fitting of at least the ring disposed on the gearbox side would then have to be done before the flange is positioned on the gearbox.
Now, such positioning consists in forced axial fitting together of complementary splines provided respectively on the stub shaft inside the gearbox and on a cylindrical sleeve extending the flange such force fitting can only be carried out with the flange off load.
The special insert plate must have a certain thickness since it is to transmit the whole of the engine torque of the vehicle from the cardan joint to the gearbox flange.
Thus, it has the double drawback of a respectively high weight and axial size.
This latter drawback may be serious in the case of very short transmissions, namely in which a limited space is available between the output of the gearbox and the input of the rear axle.
This is in particular the case for certain modern rear-engined buses, in which the overall length of the engine-gearbox assembly and that of the rear axle, particularly of the hypoid type, increase without the respective positions of these members being modified.
In such a case, it is sometimes very precious to be able to reduce, even by a few centimetres only, the extension of the transmission due to the fitting of an electric retarder of the above kind thereon, the possibility of fitting such a retarder being sometimes related directly to such a reduction.
To reduce the extension mentioned, it has already been proposed by the Applicant U.S. Pat. No. 5,044,228 to enlarge the gearbox flange transversely and to fix the rotor rings of the retarder on the periphery of this enlarged flange via a tubular insert extending axially from this periphery on the side opposite the gearbox.
The end flange of the cardan joint considered is then fixed directly to the gearbox flange, inside said tubular insert.
Such a construction is advantageous, in particular because the insert, which only has to transmit retarding torques and not drive torques, may be formed by a very light part, comprising essentially a tube section reinforced by internal radial ribs.
But it pre-supposes that the opening freed in the centre of the retarder has a large diameter, this opening having to be sufficient to receive concentrically the tubular insert and, thereinside, the flange of the cardan joint.